Smoke Signals

Smoke Signals

What’s next, a Senate inquiry into infrasound from trees, waves or air conditioners?

Infrasound is generated by wind turbines, air conditioners, and a host of natural phenomena. Johan Swanepoel/Shutterstock

At the centre of claims about wind farms allegedly causing health problems is the infrasound that wind turbines generate as they turn in the wind.

Infrasound is sound below 20Hz, which is generally inaudible. Wind turbines are just one source of artificial man-made infrasound. Others include power stations, industry generally, motor vehicle engines, compressors, aircraft, ventilation and air conditioning units, and loudspeaker systems. Everyone living in an urban environment is bathed in infrasound for most of their lives.

As I sit at my inner Sydney desk writing this I’m copping infrasound from the planes that pass some 200-300 metres over my house sometimes many times an hour, the sound of passing road traffic on a quite busy road 100 metres from our house, and the stereo system I listen to as I write. Don’t tell anyone, but I feel fine and I’ve lived here 25 years.

But infrasound is generated by natural phenomena too. These include rare occurrences such as volcanoes and earthquakes, but also sources like ocean waves and air turbulence (wind) that countless millions, if not billions, are exposed to on most days. Anyone living close to the sea is surrounded by constant infrasound from waves.

The inclusion of wind as a source of infrasound is of particular significance to claims made that wind turbine-generated infrasound is noxious. In a Polish research paper published in 2014, the authors set out to measure infrasound from wind turbines and to compare that with naturally occurring infrasound from wind in trees near houses and from the sound of the sea in and around a house near the seaside.

The researchers used the average G-weighted level (LGeq) over the measurement period. This is the standardised measurement of infrasound which approximately follows the hearing threshold below 20Hz and cuts off sharply above 20Hz.

The infrasound levels recorded near 25 100-metre high wind turbines ranged from 66.9 to 88.8 LGeq across different recordings. Those recording infrasound in noise from wind in a forest near houses ranged from 59.1- 87.8 LGeq. The recordings of sea noise near seaside houses ranged from 64.3 to 89.1 LGeq. These infrasound levels were thus very similar cross the three locations.

The peak 88.8 LGeq was recorded very close to the turbines – virtually directly under the blades. The lower 66.9LGeq was 500m away, which is more like a common scenario for the nearest residences to turbines. Similarly, for the other sources, highest levels were nearest the source.

Wind is, of course, a prerequisite for wind turbines to turn and generate their mechanical infrasound. Here, the Polish authors noted that:

natural noise sources … always accompany the work of wind turbines and in such cases they constitute an acoustic background, impossible to eliminate during noise measurement of wind turbines.

This is a fundamentally important insight: wherever there are wind turbines generating infrasound, there is also wind itself generating infrasound. And it is impossible to disentangle the two. Indeed, every time I’ve been near wind turbines, easily the most dominant sound has been that of the wind buffeting my ears.

In 2013, the South Australian Environmental Protection Authority measured infrasound in a variety of urban and rural settings. With the latter, this included locations near and well away from wind farms.

They reported that in urban settings, measured infrasound ranged between 60-70 decibels. In fact, at two locations – the EPA’s own offices and an office with a low frequency noise complaint – building air conditioning systems were identified as significant sources of infrasound. These locations exhibited some of the highest levels of infrasound measured during the study.

They concluded:

This study concludes that the level of infrasound at houses near the wind turbines assessed is no greater than that experienced in other urban and rural environments, and that the contribution of wind turbines to the measured infrasound levels is insignificant in comparison with the background level of infrasound in the environment.

Wind farm opponents claim infrasound is the cause of this Old Testament-like plague of plagues (now numbering 244 different problems). If that were true, how is it that hundreds of thousands of Australians who are daily exposed to infrasound in cities, in their houses surrounded by dastardly infrasound-generating fans, air conditioners and stereo systems, and those who live near trees or the sound of the ocean aren’t breaking down the door of those sworn enemies of infrasound Senators John Madigan, Nick Xenophon, Chris Back, David Leyonhjelm and Bob Day who brought us their scathing report on wind farms in June?

The explanation lies in factors we recognise frequently in risk-perception studies, popularised by Peter Sandman. Sandman has produced matrices of factors which have been often found to be associated with increased levels of community “outrage” about putative environmental threats to health.

Sandman distinguishes primary from additional factors, with primary factors being those which have been shown to be more strongly associated with increased levels of community concern.

I applied these to a case study of mobile phone tower complaints in the 1990s. I’ve now constructed the table below indicating the likely applicability of these factors to the case of predicting community worry about wind farms.

People don’t worry about infrasound in wind, trees and ocean waves because these sources are natural, while the same levels of infrasound from wind turbines are considered quite differently as they are sourced from what anti-wind farm activists like to call evil “industrial” wind farms.

The rare examples of people complaining who host wind turbines on their land for rental payment, compared with the far more common situation of non-hosting neighbours complaining, illustrates the voluntary vs coerced exposure factor, as well as the fair vs unfair factor. Those not benefiting from lucrative rental payments because of unsuitable local topography, while near neighbours can, understandably feel this as unfair.

Wind turbines are very memorable and exotic (a new experience to many), while wind in trees or the pounding of the ocean is very familiar and unremarkable, both factors likely to greatly diminish concerns.

Table: Primary and additional components predicting community outrage about putative environmental risks to health: the case of wind turbines. (two ticks = applies strongly to wind turbines; one tick = likely to apply less strongly)

The 2015 Senate (majority) report into wind farms roundly rejected the idea that psychosocial factors such as nocebo effects were largely responsible for the challenging historical and geographical variance in wind farm complaints. A nocebo effect is the opposite to a placebo effect: instead of exposure to an inactive agent making people feel better because of belief that it will, nocebo effects are when a benign agent makes people feel worse because they have been told it will.

The Committee, chaired by avowed wind farm opponent John Madigan, was emphatic that infrasound was the culprit but did not produce convincing evidence for this.

If the committee is sincere in its concerns about the health effects of infrasound, will we soon learn of a new inquiry about the pernicious and unappreciated dangers of living near the sea or trees, having air conditioners, stereos, ceiling fans, or travelling in motor vehicles?